Filament Spool Remaining Calculator

Why Tare Weight Matters (and Varies)

A scale can only tell you the weight of the spool and the filament together. To find how much filament is actually left, you have to subtract the weight of the empty spool itself — its tare weight. That single number is the whole game: get it right and your remaining-filament figure is trustworthy; get it wrong and every result is off by exactly the same margin. The catch is that tare weight is not standard. A lightweight cardboard spool can weigh around 150g, a generic injection- moulded plastic spool about 200g, and heavier branded spools anywhere from 215g to 250g, because spool diameter, wall thickness, material, and even production run all change the empty weight. Two spools that look nearly identical on the shelf can differ by 50g or more — and 50g of PLA is roughly 16 metres of 1.75mm filament, easily the difference between a print finishing or failing halfway. That's why this calculator leans on a per-brand tare list rather than one blanket number, and why weighing your own empty spool beats any reference table. It's also why the same 550g reading can mean quite different amounts of usable filament from one spool to the next: the number on the scale is shared between the plastic (or cardboard) and the filament, and only an accurate tare tells you where the split actually falls.

How to Use This Calculator

Put the whole spool on a scale and enter that figure as the current spool weight. Pick your spool's brand from the tare-weight dropdown to subtract an approximate empty weight, or choose "Custom" to type in a tare you've weighed yourself. Select the filament material and diameter so the length estimate uses the right density, and the calculator shows the remaining filament in grams and its approximate length in metres. If you also enter the original filament weight — commonly 1000g for a 1kg spool — it adds a percentage remaining; leave it blank and it simply omits the percentage rather than showing a misleading zero. Nothing is stored between visits, so it's a quick check you run whenever you want to know whether a spool has enough left for the job in front of you.

How to Weigh a Spool Accurately

A basic digital kitchen scale is all you need — most read to the nearest gram and cost very little. Set it to grams, wait for it to settle to zero before loading the spool, and place the spool flat and centred so its full weight sits on the platform. If the spool is wider than the scale, rest it on an upturned bowl or a light box and tare (zero) the scale with that support already in place, so you're only measuring the spool. The single most valuable habit: the next time a spool runs completely empty, weigh the bare spool once and write that number on it in marker (or keep a short note by brand). A weighed tare is exact, unlike any reference figure, and it turns every future measurement of that spool type into a precise reading. It only takes a moment and it pays off for the entire life of your filament collection. For a rough sanity check without any weighing at all, a brand-new 1kg spool of 1.75mm PLA holds roughly 330 metres of filament, so a spool reading about half its filament weight should show a length in that ballpark — if your result is wildly different, revisit the tare weight or the material you selected before trusting it.

Common Empty Spool (Tare) Weights by Brand

These are approximate reference values, not exact specifications — spool designs get revised and vary between colours and production runs, so treat them as a sensible starting point and weigh your own empty spool whenever you can for the most accurate result.

Common Mistakes

• Using a generic tare when a specific one exists. Defaulting to a round 200g when your spool is a 246g branded one throws the result off by ~46g — pick the matching brand or weigh the spool empty.
• Assuming equal weight means equal length across materials. 200g of PLA and 200g of PETG hold different lengths because their densities differ. Always select the actual material so the length reflects it.
• Forgetting to zero the scale with a support. If a wide spool rests on a bowl, tare that bowl to zero first — otherwise its weight lands in your reading and inflates the remaining filament.
• Trusting the percentage without the original weight. Percent remaining needs the new-spool filament weight. Without it the tool shows no percentage on purpose, rather than a misleading figure.
• Reading a below-tare scale as negative. If the reading is at or under the tare weight, remaining filament is treated as zero — a spool can't hold a negative amount, so that just means it's effectively empty.

Frequently Asked Questions

Know what's left, then plan the next print: the Filament Usage Estimator tells you how much a model will use before you start, and the Print Cost Calculator turns that filament into a true per-print cost.